docs: def _random_best_expander(fringe, iteration, viewer):
      '''
      Expander that expands one randomly chosen nodes on the fringe that
      is better than the current (first) node.
      '''
      current = fringe[0]
      neighbors = current.expand(local_search=True)
      if viewer:
          viewer.event('expanded', [current], [neighbors])
  
      betters = [n for n in neighbors
                 if n.value > current.value]
      if betters:
          chosen = random.choice(betters)
          if viewer:
              viewer.event('chosen_node', chosen)
          fringe.append(chosen)